Q I'm having trouble getting my wide-angle panoramas to stitch together. I'm using 24mm and 17mm wide-angle lenses. What's the trick to get these images to match up?
Salt Lake City, Utah
This 10-image panorama of the Los Osos Oaks State Nature Reserve was taken with a Canon EF 17-40mm ƒ/4L lens at 17mm. By rotating around the center of the lens instead of from under the camera, the images matched up when stitched.
A I've said for years that the secret for addressing the parallax problem (the displacement effect of viewing objects along different lines of sight) in wide-angle panoramas is to rotate the lens around its nodal point, where the light paths converge before hitting the film or sensor. Recent discussion seeks to move us toward using the term "entrance pupil" as the location on which you should center the rotation of the lens on the tripod. Whatever you call it, the point you're seeking is the approximate center of the lens from front to back. You'll need a slider under the camera to position the lens on the tripod properly over the rotation point. If you're rotating around the back or center of the camera, rather than the lens, the images won't line up properly. This calculation isn't particularly important when photographing panoramas with a telephoto lens; however, many telephotos have a tripod collar that helps to position the lens close to the optimal rotation point.
See The Sharpness
I just returned from teaching a Canon Live Learning Workshop (learn.usa.canon.com/live_learning/workshop_main.shtml) in southwestern Colorado. During a field session, one of the participants called me over to check a composition through the camera. My first conclusion was that the camera/lens wasn't properly focused, so I asked the student if she had adjusted the viewfinder for corrective lenses or contacts. She had not, but said she did normally wear eyeglasses, although not to photograph. The student's strategy was to rely on the camera's autofocus function to achieve sharp focus in every instance, because whether or not she was wearing her glasses to photograph, the image she saw in the viewfinder was blurry. As a result, she was never able to critically judge the sharpness of focus or the positioning of the focus in her image.
Together, we adjusted the viewfinder diopter in her camera until the image in the viewfinder was sharp when she was wearing her glasses and looking through the area of the lens corrected for distance. We possibly could have made the adjustment to achieve sharpness without corrective lenses, but that depends on the individual's vision challenges. Using her glasses, and with the diopter properly set, this photographer was for the first time able to work in manual focus mode and to critically judge the sharpness, and position of sharpness, being rendered by the autofocus function.
This isn't an uncommon situation. Either people don't know they can correct the viewfinder, or they don't want to make the effort to use this very important feature of their DSLRs. To adjust your diopter to make the best match between your vision and the autofocus, find a subject with contrast, use the autofocus to attain sharp focus, and then adjust the setting on the viewfinder to make the image sharp to your vision. If you wear corrective lenses, look through the area of your glasses that corrects for distance.
I also see a lot of photographers taking pictures with sunglasses in place. Yes, we're out in the field doing nature photography, and sunglasses, sometimes prescription sunglasses, are the eyewear of choice in those circumstances. Unfortunately, sunglasses cut the light by a factor of several ƒ-stops, depending on darkness and polarization. Whatever lens is mounted, your camera uses the maximum lens aperture (that is, wide open) for the focusing function. Otherwise, if you're shooting stopped down for critical focus, you would be looking through a very dark viewfinder. Critical focus is helped by having a lens with a wide aperture for a bright viewfinder. If you're wearing dark sunglasses, you're undermining this sophisticated function of your DSLR and diminishing your chances for critical focus.
When taking landscape or macro images that entail a camera on a tripod and an unmoving subject, I highly recommend using the Live View feature on your DSLR if you have it. Couple that with a loupe (I use one made by Hoodman, www.hoodmanusa.com) to critically view the LCD screen in the bright light. Use the magnification function on the LCD to check focus up to 10X.
In our quest for sharpness, we purchase special lenses, use lower ISOs and work from tripods. It's important to also make sure we're seeing the best image the camera offers.
Get The Most From A Lens And Camera
Recently, I was cruising www.canonrumors.com, and at the top of the page were two links to articles by Roger Cicala of LensRentals.com. I recommend "How to Test a Lens" (www.canonrumors.com/tech-articles/how-to-test-a-lens/) and "This Lens is Soft" (www.canonrumors.com/tech-articles/this-lens-is-soft-and-other-myths/) to anyone interested in obtaining the best sharpness and quality from a camera/lens combination.
Roger handles hundreds of lenses at a rental agency, and has to check them before sending them out and again when they come back. His simple approach and information on testing camera/lens combinations will give photographers a better understanding of why they don't always achieve the results they expect. You don't need to be a Canon user to understand what Roger is saying, so everyone, check this out.
ND Filters For All Occasions
Q I recently purchased a Canon EOS 7D with two Canon L-series lenses. Can you recommend a neutral-density filter that won't diminish the quality I can achieve with these lenses?
Via the Internet
A There are many situations where you'll need an ND filter, and you shouldn't be afraid to add a quality piece of glass to your high-end "L" lenses. If you were to buy just one, I'd say a three-stop ND filter would cover most situations to slow down water, allow people to move in the frame or any other long-exposure effect. If you're looking for an extended effect or work in extremely bright conditions, add a 5-stop model. Lower-quality ND filters, such as the square acrylics, cause focus problems at higher focal lengths. For the best range, I use a very expensive, high-quality Singh-Ray Vari-ND filter (www.singh-ray.com) that ranges from 3 stops to 8 stops, but even it won't work beyond about 250mm on my 100-400mm zoom. Also, choose a filter large enough so that it doesn't vignette with wide-angle lenses; that is, get one larger than your largest front element and use step-up ring adapters to fit smaller lenses. My filters are 77mm and fit all my 77mm, 72mm, 67mm and 62mm lenses with step-up adapters.
Q I'm finding anomalies on my images resulting from debris on my sensor. I'm nervous about cleaning it myself. Sending it in to a repair facility takes too long and is expensive. How do you approach this problem?
Via the Internet A Even with the self-cleaning sensors, this is a problem that you simply must address regularly. Go to www.cleaningdigitalcameras.com and read the tutorials and evaluations of a wide range of sensor-cleaning methods and products. With the right information, you can do this.
Of all the possible methods, my preference is using the LensPen SensorKlear Loupe Kit (www.lenspen.com). The package includes a loupe that replaces your lens and magnifies and lights the sensor, giving you an excellent view of the debris you want to remove. To accomplish this, you insert an articulated SensorKlear II pen through the cutout on the side of the loupe, which gives you access to the sensor. The Sensor pen has a triangulated soft tip that allows you to remove debris even from the corners and edges of the sensor. I bought mine through Micro-Tools (www.micro-tools.com).
I had a note from my friend Dan Blackburn asking for help in locating images gone missing from his CF card. "We went to Arches for a sunset shoot of Balanced Rock," he wrote. "The light was very good and I used the same card that I had used earlier in the day for some mountain fall color. I also periodically checked the images in the camera as the light changed in Arches and everything looked just fine. But, when I returned home, the entire section of the card devoted to Balanced Rock was blank. The images from earlier in the day were fine. But Arches was totally missing. Any idea what could have happened?"
I advised Dan to try a file recovery software to see if the files were even written to the card, and he used SanDisk RescuePRO Deluxe (www.lc-tech.com). "It did a fine job of recovery," he reported. "Not only were the missing Arches files recovered, but also some old mule deer and other shots."
CF cards get old and corrupt and need to be thrown out. Beyond this, I do advise the purchase of quality CF and SD cards with proven records of performance. Personally, I only use RAW cards from Hoodman (www.hoodmanusa.com).
For information about upcoming seminars and digital-imaging workshops, visit www.georgelepp.com. If you have any tips or questions, address them to: OUTDOOR PHOTOGRAPHER, Dept. TT, George Lepp, 12121 Wilshire Blvd., Suite 1200, Los Angeles, CA 90025-1176 or online at www.georgelepp.com.